What is the Cause of an Earthquake?

What is the Cause of an Earthquake?

I’ve been writing about earthquake preparedness and the importance of earthquake kits but what is the cause of an earthquake?

What Causes an Earthquake?

An earthquake is caused when stress builds up between two large blocks (plates) of the earth’s crust and one of these suddenly slip past the other. The area between the plates are called faults. The earth’s crust is made of several continental and oceanic plates that are constantly rubbing/sliding past each other or pulling apart.

Think of the faults as having jagged edges, similar to how your knuckles on your hand are when you make a fist with both hands. If you gently rub your knuckles together, you can feel them getting locked in place. Then you need to add some extra force to it in order to move again. This is similar to how earthquakes occur and the sudden release of energy is what causes the earth to move and vibrate. Energy is stored up when stuck until enough force is made to move. Then, it will continue to move until it gets stuck again and the process repeats.

What Types of Earthquakes are There?

There are 3 types of faults that cause earthquakes. They can be categorized as Strike-slip, Dip-slip, and Oblique-slip. Each of these work a bit differently so I’ll explain in more detail. More recently, there have been human-induced earthquakes.

Strike Slip

Strike-Slip

This occurs when two plates are sliding horizontally past each other, similar to the knuckle experiment I mentioned earlier. An example is the Great Earthquake that struck San Francisco in 1906 an destroyed 80% of the city.

Dip-Slip

Dip-Slip

Dip-slips occur when plates are pushed towards each other and eventually one gives way and either buckles up or buckles down which can create valleys or mountains. There are two types: Normal faults and reverse faults. Normal faults has the footwall moving over the hanging wall whereas in a reverse fault the footwall goes down. Some examples created by these are the Sierra Nevada Valley, Mid-Atlantic Ridge, Rocky Mountains, and the Himalayas.

Oblique-Slip

Oblique-Slip

This is a combination of both strike-slip and dip-slip. Usually any earthquake has some horizontal and vertical movement so categorizing it as oblique-slip means that the measurement of both strike and dip to be significant. An example is the 1999 Hector Mine earthquake that hit California.

Human-Induced

Humans are incredible (both in a good way and bad). We are capable of inducing earthquakes by pumping wastewater into deep disposal wells near faults as seen in the incredible amount of earthquakes that strike the Oklahoma region every year. As oil and gas production ramps up in those areas, the number of earthquakes have risen significantly. Evidence of this is that in 2007 Oklahoma experienced only 1 earthquake while last year there were almost 900 3-plus magnitude earthquakes. For the first time, this lead the U.S. Geological Survey to publish an earthquake hazard map covering both natural and “induced” earthquakes.

 

Now that we know how an earthquake is caused, let’s see how they are located and measured in my next post.

How are Earthquakes Measured? What is Magnitude?

 

Read more about how to be prepared for an earthquake

How to Prepare for an Earthquake

10 Comments

  1. Roger

    Andy,

    Most instructive! I never really understood what did cause earthquakes. I know there’s a lot of rumbling and movement!

    I now live in New England. We don’t have so many earthquakes here, but they do occur (we had one just recently). I remember reading once that experts thought a New England quake could be a lot more destructive than a California quake, simply because New Englanders aren’t expecting quakes and so are unprepared!

    So I’ll be sure and share your website!

    Thanks for all the education.

    Roger

    Reply
    1. Andy (Post author)

      Thanks Roger! That’s true, people in California have been dealing with earthquakes for years. They have drills and training whereas the East Coast is probably much less prepared.
      It’s always a good idea to understand what to do in an earthquake just in case no matter where you are.

      Reply
  2. Kari

    Interesting read. I live in California and was around during the devastation on the 1994 earthquake in Northridge. I was unaware that earthquakes could be human induced! Crazy! You’d think that I would be prepared for an earthquake, but I don’t think I am….I definitely need to check out your “Preparedness” articles!

    Reply
    1. Andy (Post author)

      Hi Kari, glad my site can be helpful and hopefully others will benefit as well.

      Reply
  3. Helen Doyle

    Andy, we do live on the Pacific rim but fortunately for us most quakes occur to the east and north east of us. We do get the odd tremor but often attribute that to forestry blowing up ‘dangerous’ trees. So the sound impact of a quake isn’t often noticed. You didn’t mention the devastating earthquakes in Christchurch, NZ over the last few years. That did a lot of damage. And you have confirmed what I have thought for years. We humans can not keep doing what we are doing without these disasters increasing. Hope the message doesn’t continue to fall on deaf ears!

    Reply
    1. Andy (Post author)

      Thanks Helen! Yes, I did miss the Christchurch quake. Maybe I will write about it in a future post. I agree, it’s pretty horrible how us humans are taken over by greed and are willing to do anything, even damage the earth and put other people’s lives in danger. Hopefully people will do something about it soon.

      Reply
  4. Green

    Hello Andy- Just as I was wondering why would you do a website on earthquakes it hit me to go to your “about me” page. First of all, I would be scared to death an 8.0 earthquake oh man, I think it would be time for me to relocate for a while. I think it is awesome that not only are you explaining how they happen, but you are providing recourse for people that (choose to stay) if it happens e.g. the earthquake kits, awesome idea! Well, good luck and be safe Andy!
    Sherry

    Reply
    1. Andy (Post author)

      Thanks Sherry!

      Yeah it’s not easy for some people to just relocate because of certain factors like family, job, living standards, and cost of living so the best thing is to be prepared and know what to do in an earthquake. Even if you don’t live in an earthquake zone, you never know if you’ll ever travel or vacation to one so it’s always a good idea to be prepared.

      Reply
  5. Jeffrey

    Nice read…great content. I am waiting for the technology that would be able to reliably predict an earthquake. Keep up the good work.

    Regards,
    Jeff

    Reply
    1. Andy (Post author)

      Thanks Jeffrey!
      Yeah I wish they can predict earthquakes in advance. That would definitely save a lot of lives.

      Reply

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